Device for controlling and balancing currents for dc/dc converters

ABSTRACT

The invention provides a control device for regulating and balancing currents, for DC/DC converters, between first and second voltage sources, the device comprising: n converters (C 1,  C 2, . . .  Cn) that are connected in parallel to the first voltage source ( 11 ); n inductors (L 1,  L 2, . . .  Ln) that have their outlets connected to the second voltage source (R) via n connections; n current sensors ( 22 ) that are arranged on respective ones of the connections; and a single regulator system that has its inputs connected to respective ones of the n current sensors ( 22 ), and its output connected to the n converters (C 1,  C 2, . . .  Cn).

TECHNICAL FIELD

The invention relates to a control device for regulating and balancingcurrents for DC/DC converters, in particular in the field of energystorage, e.g. for charging and discharging batteries.

STATE OF THE PRIOR ART

FIG. 1 shows a prior-art high-power DC/DC converter including n armseach made up of two semi-conductor components arranged in series. Eachsemi-conductor component comprises a transistor Ti, e.g. an insulatedgate bipolar transistor (IGBT) in parallel with a diode Di. Theconverter is arranged between a storage unit 11, e.g. a battery, and aload voltage source R, the middle point of each arm, corresponding to arespective phase i of the current, being connected to the load voltagesource R by means of a respective smoothing inductor L1, L2, . . . Ln.The converter also includes a regulator system that is made up ofrespective proportional integral derivative blocks PIDi and respectivepulse width modulation blocks PWMi for each current phase i, the currentIi* representing a current setpoint.

A regulator system PIDi+PWMi is described below.

PID Block

A PID block, shown in FIG. 2, serves to regulate a value, i.e. toconstrain a system to follow a given setpoint by providing closed-loopfeedback. The value to be regulated is thus monitored and compared tothe given setpoint, and the difference between them is measured. Anoutput signal is then generated that is proportional to said difference.But the proportional gain is not sufficient, since the setpoint valuemay be overshot because of the inertia of the system. Thus, in order topredict the behavior of the system, the output value is integrated. Ifthe setpoint value is overshot, the integrator constrains the system toadapt the output. Furthermore, since this integral gain is notsufficient, the slope (derivative) is monitored so as to check that thesetpoint is not overshot, and if it is, a correction is made.

All of these regulation techniques constitute a PID corrector. Thus, thetransfer function of a parallel PID corrector, as a Laplace transform,is the sum of three actions:

${C(p)} = {G + {\frac{1}{\tau \; i} \cdot \frac{1}{p}} + {{Td} \cdot p}}$

PWM Block

A PWM block uses pulse width modulation that consists in introducingadditional switching at frequency that is higher than the fundamentalfrequency, transforming a voltage into a series of square waves of fixedamplitude and of varying width. A PWM command is obtained by comparing alow-frequency modulating wave 20 to a high-frequency carrier wave 21 oftriangular waveform, as shown in FIG. 3. The pulses S as generated inthis way serve as commands for switching transistors Ti.

Using a regulator system for each phase of current to be regulatedrequires the regulator system to be replicated as many times asnecessary, and this leads to a large consumption of resources. For anembodiment with field programmable gate array (FPGA) circuits, thisleads to a greater number of logic gates.

To solve this technical problem, the invention proposes a control devicefor regulating and balancing currents for n DC/DC converters using asingle regulator system, with balanced currents, as shown in FIG. 4, sothat: I=I1+I2+ . . . In and I1=I2= . . . In

SUMMARY OF THE INVENTION

The invention provides a control device for regulating and balancingcurrents, for DC/DC converters, between first and second voltagesources, the device comprising:

-   -   n converters that are connected in parallel to the first voltage        source;    -   n inductors that have their outlets connected to the second        voltage source via n connections; and    -   n current sensors that are arranged on respective ones of the        connections;    -   a single regulator system that has its inputs connected to        respective ones of the n current sensors, and its output        connected to the n converters;        characterized in that the regulator system comprises:    -   a summing circuit for summing the currents output from the        current sensors;    -   a PID block that receives the current output from the summing        circuit;    -   a 1/n divider that receives the current output from the summing        circuit and that delivers an average current;    -   n comparators for comparing the currents measured by the current        sensors with the average current;    -   n proportional gain elements that are arranged at the outputs        from the comparators;    -   n summing circuits for summing the outputs from the n        proportional gain elements with the output from the PID block;        and    -   a PWM block that receives the outputs from the n summing        circuits and that delivers n interleaved channels.

The device of the invention presents the following advantages:

-   -   a regulated average current is used from the n arms;    -   the currents from the n arms are balanced;    -   a single regulator system is used;    -   rapid balancing is obtained as a result of the contribution from        the proportional correction;    -   current sensors are used that are calibrated for (1/n)^(th) of        the average current; and    -   execution times are short and FPGA resources are minimal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior-art device.

FIG. 2 shows a PID block.

FIG. 3 shows the operation of a PWM block.

FIGS. 4 and 5 show characteristics of the device of the invention.

FIGS. 6 and 6A show an embodiment of the device of the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

In the description below, elements that are analogous to one another areshown with the same references.

The control device of the invention for regulating and balancingcurrents for DC/DC converters, as shown in FIGS. 4 and 5, comprises:

-   -   n boost/buck converters C1, C2, . . . Cn that have their inlets        connected to a voltage source 11 that delivers or absorbs        energy;    -   n inductors L1, L2, . . . Ln that have their inlets connected to        the outlets of respective ones of the converters C1, C2, . . .        Cn, and that have their outlets connected via n connections and        a summing circuit 12, to a load voltage source R that delivers        or absorbs energy;    -   n current sensors 22 that are arranged on respective ones of the        connections; and    -   a regulator system 28 comprising:        -   a summing circuit 24 for summing the currents output from            the current sensors 22;        -   a PID block arranged at the output from the summing circuit;        -   a 1/n divider 25 that receives the current output from the            summing circuit and that delivers an average current;        -   n comparators 26 for comparing the currents measured by the            current sensors 22 with the average current;        -   n proportional gain elements 23 that are arranged at the            outputs from the n comparators;        -   n summing circuits 27 for summing the outputs from the n            proportional gain elements with the output from the PID            block; and        -   a PWM block that receives the outputs from the n summing            circuits and that delivers n interleaved channels.

In the device of the invention, the average value of the sum of theoutlet currents from the DC/DC conversion device is regulated, and thisrequires only one regulator system. The currents of the n converters ofthe DC/DC conversion device are balanced by measuring the outletcurrents and by comparing them to the average value (divided by n).Thus, the resulting difference is added, via a proportional gain, to thecommand for regulating the average value.

The device makes it possible to use only one regulator system and toensure that the currents are balanced.

FIGS. 6 and 6A show a solution tested on a 500 kilowatt (kW) energystorage demonstrator with Li-ion batteries and NaS batteries. Thestructure used corresponds to a basic structure comprising a DC/DCconverter 30 and a DC/AC converter 31 situated between the battery 32and the AC network 33, three-phase windings 34 and 35 being arranged atthe inlets and at the outlets, capacitance being arranged between aDC/DC converter and a DC/AC converter. The curves 36 show the currentsof two of the three DC/DC converters, and the curve 37 shows the totalcurrent.

What is claimed is:
 1. (canceled)
 2. A control device for regulating andbalancing currents, for DC/DC converters, between first and secondvoltage sources, the device comprising: n converters that are connectedin parallel to the first voltage source; n inductors that have theiroutlets connected to the second voltage source via n connections; and ncurrent sensors that are arranged on respective ones of the connections;a single regulator system that has its inputs connected to respectiveones of the n current sensors, and its output connected to the nconverters, wherein the regulator system comprises: a summing circuitfor summing the currents output from the current sensors; a PID blockthat receives the current output from the summing circuit; a 1/n dividerthat receives the current output from the summing circuit and thatdelivers an average current; n comparators for comparing the currentsmeasured by the current sensors with the average current; n proportionalgain elements that are arranged at the outputs from the comparators; nsumming circuits for summing the outputs from the n proportional gainelements with the output from the PID block; and a PWM block thatreceives the outputs from the n summing circuits and that delivers ninterleaved channels.